Presence Of Wind Turbines Research Articles

Robust Power Management Control for Stand-Alone Hybrid Power Generation System

This paper presents a new robust fuzzy control of energy management strategy for the stand-alone hybrid power systems. It consists of two levels named centralized fuzzy supervisory control which generates the power references for each decentralized robust fuzzy control. Hybrid power systems comprises: a photovoltaic panel and wind turbine as renewable sources, a micro turbine generator and a battery storage system. The proposed control strategy is able to satisfy the load requirements based on a fuzzy supervisor controller and manage power flows between the different energy sources and the storage unit by respecting the state of charge and the variation of wind speed and irradiance. Centralized controller is designed based on If-Then fuzzy rules to manage and optimize the hybrid power system production by generating the reference power for photovoltaic panel and wind turbine. Decentralized controller is based on the Takagi-Sugeno fuzzy model and permits us to stabilize each photovoltaic panel and wind turbine in presence of disturbances and parametric uncertainties and to optimize the tracking reference which is given by the centralized controller level. The sufficient conditions stability are formulated in the format of linear matrix inequalities using the Lyapunov stability theory. The effectiveness of the proposed Strategy is finally demonstrated through a SAHPS (stand-alone hybrid power systems) to illustrate the effectiveness of the overall proposed method.

An analysis of premature cracking associated with microstructural alterations in an AISI 52100 failed wind turbine bearing using X-ray tomography

Crack surrounded by local areas of microstructural alteration deemed “White etching cracks” (WECs) lead to unpredictable and premature failures within a multitude of applications including wind turbine gearbox bearings. While the exact cause of these failures remains unknown, a large number of hypotheses exist as to how and why these cracks form. The aim of the current work is to elucidate some of these hypotheses by mapping WEC networks within failed wind turbine bearings using high energy X-ray tomography, in an attempt to determine the location of WEC initiation, and the role of defects within the steel, such as inclusions or carbide clusters. Four completely subsurface WECs were found throughout the presented analysis, thereby confirming subsurface initiation as method of WEC formation. Additionally, a multitude of small butterfly like cracks were found around inclusions in the steel, however further analysis is needed to verify if these inclusions are initiation sites for WECs.

Experimental and Simulation Studies of Strength and Fracture Behaviors of Wind Turbine Bearing Steel Processed by High Pressure Torsion

White structure flaking (WSF) has been found to be one of the failure modes in bearing steels under rolling contacts through the formation of cracks associated with a microstructural change called white etching area (WEA). In the present research, the effects of the high-pressure torsion (HPT) process on the microstructure and mechanical properties of an AISI 52100 alloy are studied. An annealed AISI 52100 was subjected to high-pressure torsion at room temperature under a pressure of up to ~6 GPa for up to three turns. Finite-element modeling (FEM) was used to simulate the process under high-pressure torsion and quasi-constrained conditions to reveal the material property changes occurring in HPT. Scanning electron microscopy and microhardness testing after processing were used to investigate the microstructural and mechanical property evolution of the steel. Strain induced microstructural transformations occur and affect the mechanical properties in a similar way to the well-known white etching area (WEA) found beneath the surface of wind turbine bearings. Here, HPT is used to study the feasibility of creating microstructural changes that are similar to WEA. This paper presents the preliminary results of using HPT to produce WEAs.

Does the presence of wind turbines have negative externalities for people in their surroundings? Evidence from well-being data

Throughout the world, governments foster the deployment of wind power to mitigate negative externalities of conventional electricity generation, notably CO2 emissions. Wind turbines, however, are not free of externalities themselves, particularly interference with landscape aesthetics. We quantify these negative externalities using the life satisfaction approach. To this end, we combine household data from the German Socio-Economic Panel Study (SOEP) with a novel panel dataset on over 20,000 installations. Based on geographical coordinates and construction dates, we establish causality in a difference-in-differences design. Matching techniques drawing on exogenous weather data and geographical locations of residence ensure common trend behaviour. We show that the construction of wind turbines close to households exerts significant negative external effects on residential well-being, although they seem both spatially and temporally limited, being restricted to about 4000m around households and decaying after five years at the latest. Robustness checks, including view shed analyses based on digital terrain models and placebo regressions, confirm our results.

Fault diagnosis method for spherical roller bearing of wind turbine based on variational mode decomposition and singular value decomposition

For the non-stationary characteristics of the vibration signal of wind turbine’s roller bearing in fault condition, a bearing fault diagnosis method based on variational mode decomposition (VMD) and singular value decomposition (SVD) is proposed. The VMD method is used to decompose wind turbine’s roller bearing’s fault vibration signal into several components. These components are regard as initial feature vector matrix. The singular value decomposition of the matrix is done. The obtained singular value is used as the extracted bearing fault feature vectors. The probabilistic neural network is used as pattern recognition classifier to determine the working state and fault type of wind turbine roller bearings. The result of case study showed that the proposed method can effectively identify the working state and fault type of wind turbine roller bearings.

Comparison of Life Calculations for Oscillating Bearings Considering Individual Pitch Control in Wind Turbines

The fatigue life calculation of bearings under rotating conditions has been well researched and standardized. In contrast, for bearings in oscillating applications no international standards exist. As a result, pitch bearings in wind turbines are designed with different, non standardized approaches. Furthermore, the impact of individual pitch control on pitch bearings has not yet been studied. In this paper four approaches for fatigue life calculation will be applied and compared under individual pitch control conditions. For comparison, the loads and the bearing geometry of the reference turbine IWT 7.5 MW, which is individual pitch controlled, are used. This paper will show how the bearing life calculated by different approaches reacts to individual pitch control conditions. Furthermore, the factors for the modified rating life, according to the ABMA and ISO standards, which implement different operation conditions on the bearings in rotating applications, are calculated for the given loads and the given bearing geometry in oscillating applications.

Investigation on the mechanisms of white etching crack (WEC) formation in rolling contact fatigue and identification of a root cause for bearing premature failure

This paper reports on a study that has resulted in the identification of one of the root causes for bearing premature failure characterized by sub-surface ‘white etching’ cracks (WEC) and surface axial cracks leading to spalling on ring raceways. Failure analysis performed on some failed rolling bearings used in wind turbines revealed fretting corrosion bands on the inner ring bore having positions that coincide circumferentially with zones of sub-surface WECs and surface axial cracks on the raceways. Appearance of fretting corrosion bands on the bearing bore is an indication of bearing seat form deviation. It was demonstrated by FE simulation that bearing seat form deviation such as waviness can result in tensile stress near raceway, which, if exceeding a certain limit, can weaken the material and, in combination with Hertzian stress, result in early initiation and accelerated growth of cracks from the pre-existing material defects, leading to premature failure of the bearing. Rubbing between the crack faces during subsurface crack propagation causes microstructure alteration of the crack surfaces and the formation of WECs. The tensile stress drives the propagation of the subsurface cracks towards raceway, leading to occurrence of the surface-breaking cracks or the so-called “hair-line” axial cracks, and eventually spalling of the ring raceway. A specially designed bearing test has successfully reproduced the failure mode occurring in prematurely failed bearings in wind turbine gearbox. Such a test involves a wavy sleeve shaft that results in sufficiently high tensile stresses in the raceway region of a cylindrical roller bearing inner ring. All tested bearings failed prematurely under a relatively low-load due to axial cracks on the raceway surface with associated clusters of sub-surface white etching cracks, i.e. the mode of failure that is commonly representative for wind turbine bearings.

A New Load-shedding Approach for Microgrids in the Presence of Wind Turbines

Following the penetration of microgrids in distribution systems, frequency deviations in contingency conditions are becoming increasingly important. Therefore, effective load shedding is necessary to regulate the frequency. This article develops a new load-shedding method for microgrids considering wind speed changes. The proposed method uses a combination of frequency and voltage data for determining load-shedding amounts in each contingency condition. For this purpose, the total required load shedding is determined first by using transient stability analysis in different contingency scenarios in microgrids. This will establish a database for an adaptive neuro-fuzzy inference system network to determine the total required load shedding. Then a fuzzy system is used to determine the load shedding in each step dynamically based on the severity of contingencies. The proposed method capability is compared with the conventional load-shedding method. Simulation results show the effectiveness of the proposed method for microgrid control in contingency conditions.

Wind turbine bearing fault diagnosis based on adaptive local iterative filtering and approximate entropy

For the unsteady characteristics of a fault vibration signal from a wind turbine rolling bearing, a bearing fault diagnosis method based on adaptive local iterative filtering and approximate entropy is proposed. The adaptive local iterative filtering method is used to decompose original vibration signals into a finite number of stationary components. The components which comprise major fault information are selected for further analysis. The approximate entropy of the selected components is calculated as a fault feature value and input to a fault classifier. The classifier is based on the nearest neighbor algorithm. The vibration signals from a spherical roller bearing on a wind turbine in its normal state, with an outer race fault, an inner race fault and a roller fault are analyzed. The results show that the proposed method can accurately and efficiently identify the fault modes present in the rolling bearings of a wind turbine.

Vibration condition monitoring system for wind turbine bearings based on noise suppression with multi-point data fusion

A noise suppression method for feature frequency extraction that is supplemented with multi-point data fusion was investigated in consideration of issues involving wind turbine vibration signals subject to high noise disturbance. The difficulty of extracting early weak fault features was examined as well. First, a de-noising and feature extraction method that uses EMD-Correlation was developed by adding empirical mode decomposition (EMD) and autocorrelation de-noising to the wavelet package transform under the effects of white noise and short-term disturbance noise in wind turbine vibration signals. Second, an EMD-Correlation analysis model for feature frequency extraction supplemented with multi-point data fusion was established with reference to adaptive resonance theory-2 to highlight the feature frequency of a possible early weak fault. Third, the results obtained with the actual and simulated fault vibration signals of wind turbine bearing faults and the outcomes of comparing the different feature frequency extraction methods show that the proposed method of EMD-Correlation that is supplemented with multi-point data fusion can not only effectively reduce white noise and short-term disturbance noise but can also extract the feature frequency of early weak faults. Finally, prototype hardware and software were developed for a wind turbine condition monitoring system based on the aforementioned fault feature extraction algorithms and tested in an actual wind turbine generation system.

Dynamic life prediction of pitch and yaw bearings for wind turbine

The design guideline of the National Renewable Energy Laboratory (NREL) is a standard for designing and verifying pitch and yaw bearings of wind turbines. The usability of the guideline was evaluated by comparing with analytical results obtained by a commercial software. Results from calculation equations of the NREL guideline and from a commercial software were compared in terms of the main design evaluation items of pitch and yaw bearings, such as dynamic life, static load factor, and case-core interface models. Calculation and analysis were conducted using specifications and loading conditions for the yaw bearing of a 2.5 MW wind turbine. Results showed that the values computed using the NREL guideline were more conservative than those derived using the commercial software. Although the guideline showed some differences from the analytical results obtained using the software, they can be used in the initial design of pitch and yaw bearings because of the advantage of the simplicity and the characteristics of conservative output.

A proactive group maintenance policy for continuously monitored deteriorating systems: Application to offshore wind turbines

This article presents an optimum proactive group maintenance policy for continuously monitored systems affected by stochastic deterioration (degradation). A system is composed of multiple nonidentical subsystems, each exposed to a gradual degradation phenomenon. When the length (or size) of degradation in a subsystem reaches a predetermined fault threshold, it fails and leads to failure of the whole system. In order to avoid system failures and to improve availability levels, a proactive group maintenance task is conducted once the degradation level of a subsystem exceeds an “alert” threshold (smaller than the fault threshold). In this maintenance task, the critical subsystem undergoes a state-dependent repair action, and a preventive maintenance is performed on the other subsystems. Furthermore, the whole system is preventively replaced because of safety requirements when its operational age attains a fixed value. We formulate a multivariate nonlinear maintenance optimization model to simultaneously determine the optimal alert thresholds for subsystems and the replacement time for system. The performance of the proposed maintenance policy, regarding the objective of minimum system’s average long-run maintenance cost per unit time, is compared to five conventional cases of maintenance policies: the reactive response, individual age-based, individual condition-based, bivariate age- and condition-based, and age-based group maintenance. A numerical example, using real-life data collected from an offshore wind dataset, is presented to illustrate the applicability of the proposed model to the maintenance of a group of wind turbine bearings.

Critical Assessment 13: Elimination of white etching matter in bearing steels

One form of damage due to rolling contact fatigue is the formation of localised regions of extremely hard material forming within the body of a bearing. These regions have a relatively homogeneous structure and hence etch mildly with respect to the surrounding unaffected matrix. They, therefore, appear white in a darker background when examined using optical microscopy. We assess here the cause of this damage and propose solutions that are backed by evidence that already is available. The issue is important because of the spate of unexpected failures in large wind turbine bearings and of generic importance in determining the life of more well behaved bearing applications.

On the Impact of Wind Farms on a Convective Atmospheric Boundary Layer

With the rapid growth in the number of wind turbines installed worldwide, a demand exists for a clear understanding of how wind farms modify land-atmosphere exchanges. Here, we conduct three-dimensional large-eddy simulations to investigate the impact of wind farms on a convective atmospheric boundary layer. Surface temperature and heat flux are determined using a surface thermal energy balance approach, coupled with the solution of a three-dimensional heat equation in the soil. We study several cases of aligned and staggered wind farms with different streamwise and spanwise spacings. The farms consist of Siemens SWT-2.3-93 wind turbines. Results reveal that, in the presence of wind turbines, the stability of the atmospheric boundary layer is modified, the boundary-layer height is increased, and the magnitude of the surface heat flux is slightly reduced. Results also show an increase in land-surface temperature, a slight reduction in the vertically-integrated temperature, and a heterogeneous spatial distribution of the surface heat flux.

Evaluation of Quality of Life of Those Living near a Wind Farm.

Objectives: Health-related quality of life (HRQoL) can serve as a multidimensional means of evaluating the relationship between the presence of wind turbines in residential areas and their consequence for health. The purpose of this study was to determine whether a relationship exists between the presence of wind farms at different stages of development and the HRQoL of people living in their vicinity in Poland. Method: The instruments employed in this study were the SF-36v2, a questionnaire measuring self-reported health problems, and a sociodemographic questionnaire. The study involved 1277 people who lived within 2 km from a wind turbine. Results: The highest overall QoL scores were obtained by respondents living the closest to wind turbines. The mental health, role emotional, and social functioning scores were significantly higher among respondents living near wind farms and wind-farm construction sites than among those living close to locations where wind farms were planned but where construction had not yet begun. Positive correlations were found between physical and mental component scores and reactions to the news of plans to construct a wind farm. Significant differences in physical and mental component scores were observed between residents who reacted calmly and those who responded with apprehension. Residents who expected the improvement of their financial standing as a result of the wind farm assessed their general health higher than those who did not expect to receive any economic benefits. The lowest QoL scores corresponded to frequent headaches, stomach aches, and back pain over the previous three months, as well as recurrent problems with falling asleep, anxiety, and a lack of acceptance of the project. Conclusion: The lowest overall QoL and general health scores were noted among residents of places where wind-farm developments were either at the stage of planning or under construction. In order to find ways of reducing environmental stress and its adverse effects on health, it is necessary to conduct research on residents of places where a wind farm is either planned or under construction, or has just been completed.

Observations of the effect of varying Hoop stress on fatigue failure and the formation of white etching areas in hydrogen infused 100Cr6 steel rings

White etching cracks (WECs) in wind turbine gearbox bearings have been studied previously. Rolling contact fatigue (RCF) tests are conducted on 100Cr6 bearing steel rings, in this study, to generate WECs like those found in wind turbine bearings. This research studies the effect of two different levels of tensile Hoop stresses on the failure life and formation of WECs in the rings. The rings are pre-charged with hydrogen before RCF tests are conducted. It is found that these rings experience incremental fatigue failure, followed by a sudden rapid failure. The fractography, Reflecting Light Microscopy (RLM) and Scanning Electron Microscopy (SEM) results are presented in this paper.

A life test method and result analysis for slewing bearings in wind turbines

Slewing bearings generally consist of the rotational connection between two substructures and are usually used for complex load at very low speeds. If the slewing bearing has some faults during the working lifecycle, the machine will have to be stopped and the slewing bearing will be disassembled for checking the internal surface damage of the rings or rolling elements to prevent serious accidents. However, this is a very difficult process and will cost a lot of manpower, time, and money. Although there is a large number of traditional or modern techniques used widely in general bearings, they may not be able to predict the remaining service life of slewing bearings precisely due to the huge difference between the general bearings and the slewing bearings, thus, the experiments are the most effective and reliable methods. In this paper, a special test table for slewing bearings applied in wind turbine generators is presented and an accelerating fatigue life test method based on the test equipment is proposed to study the fatigue properties and predict the remaining service life of the slewing bearings used in wind turbines. It is shown that the presented test equipment can realistically reflect the state of slewing bearings under the actual working conditions. What’s more, the experimental results show that the proposed method is conservative and provides a more accurate prediction of the fatigue life for the slewing bearings and also can meet the high reliability requirements of the slewing bearings in wind turbines.

An adaptive and automated bolt tensioning system for the pitch bearing assembly of wind turbines

The assembly process of wind turbines is performed mainly manually and is characterized by unergonomic operations. In the case of the rotor blade bearing assembly three bearings, which have a diameter of several meters, are bolted to the rotor hub with hundreds of bolts. Although the introduced preload force on these bolts should be subjected to only minor deviations, the tightening process is performed manually despite its high labor intensity. Until now, low production numbers and a lack of automation concepts for large-variant components did not allow a cost-effective automation. By developing a robot guided bolt tensioning tool and adaptive tensioning process the tightening process can be automated for rotor blade bearings of wind turbines.

Micromechanical study of the effect of inclusions on fatigue failure in a roller bearing

Purpose – The purpose of this paper is to carry out a set of micromechanical analyses to study the effect of small inclusions on fatigue life of wind turbine bearings. Design/methodology/approach – The local stress concentrations around an inclusion are determined from a characteristic unit cell model containing a single inclusion, using the approximation of a 2D plane strain numerical analysis. The Dang Van multiaxial fatigue criterion is used for the local stresses in the matrix material, to ensure that the stresses remain within the fatigue limit. The matrix material is taken to be one of the most commonly used bearing steels, AISI 52100, and two different types of inclusions are considered. The macroscopic stress histories applied correspond to either a Hertzian or an elastohydrodynamic (EHL) contact pressure distribution under the rollers. Findings – The paper shows that sub-surface fatigue failure due to rolling contact is more likely to develop close to the inclusion-matrix interface, at particular angles that depend on the material and on the inclusion orientation. Originality/value – Inclusions represent an important issue in the design of wind turbine bearings, that are supposed to work in the very high cycle regime (N>109 cycles). This paper develops a micromechanical study that provides a deeper understanding on effect of inclusions on the fatigue life, according to one of the most used multiaxial fatigue criteria.

An optimal age-based group maintenance policy for multi-unit degrading systems

In order to share maintenance set-up costs and reduce system breakdown, the group maintenance policies are widely used for complex multi-unit systems. In this paper, an optimal age-based group maintenance policy is proposed for a multi-unit series system whose components are subject to different gradual degradation phenomena. When the degradation level of a component reaches a given critical size, it is replaced by a new one and the other components undergo a preventive maintenance (PM) action; otherwise, a planned group PM is performed for the whole system at operational age T>0. The problem is to determine an optimal group maintenance time T⁎ such that the system’s average long-run maintenance cost per unit time is minimized. The explicit expression of the objective function is derived and sufficient conditions for existence and uniqueness of the optimal solution are obtained. Finally, the proposed maintenance policy is applied to a group of wind turbine bearings and the results are compared with the case without planned maintenance (i.e., reactive response) and with an individual age-based maintenance policy.